public class XXXAttribute : PropertyAttribute{
	public XXXAttribute(int x, int y){
	
	}
}

[CustomPropertyDrawer(typeof(XXXAttribute))]
public class Drawer_XXXAttribute : PropertyDrawer{

	public override float GetPropertyHeight(SerializedProperty property, GUIContent label){
		... // determine attribute height occupied in inspector
	}
	
	public override OnGUI(Rect position, SerializedProperty property, GUIContent label){
		... //draw on inspector
	}

}

[XXXAttribute(1, 2)]  <-- Decorated Attribute
float values;